wads get installed into your NAND. Your system menu is in your NAND. Homebrew apps and games on SD or USB don't install into your nand so they are not nearly as risky (unless they specifically write the nand). If you never install the wad, you'll definitely be safe. I've been installing wad forwards from different sources a lot and haven't had any problems. I could be wrong but if you have priiloader properly installed, it should be fairly easy to recover if something does happen.